package Java.j1;

import java.util.Scanner;

public class AcWing_616 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        double a = sc.nextDouble();
        double b = sc.nextDouble();
        double c = sc.nextDouble();
        double d = sc.nextDouble();
        System.out.printf("%.4f",Math.sqrt((a-c)*(a-c)+(b-d)*(b-d)));
    }

}
